I recently upgraded my Sony Z3 Compact to Android Marshmallow and noticed something really odd. When not on WiFi, I wasn't getting any push notifications or any updates. I'd come home or get to work and then my phone would light up and beep like mad. Later, I discovered that there was no network connection on the mobile network. I could make calls and receive texts, but the data connections just wouldn't work. Luckily, it's an easy problem to fix.